There is known from EP Patent No 0607726 a bracelet clasp having a mechanism including a base plate hinged to the end of a strip, and an inverted U-shaped cover projecting over the base plate and whose two free edges are respectively extended on the same side by a lateral arm, the end of which is rotatably mounted on the corresponding lateral face of the base plate. The free edges of the cover can be locked by lateral locking means, the adjustable strand passes between the base plate and the cover, and is retained by a stud protruding from the inner face of the base plate or of the cover.
It is not easy for a user to operate such a mechanism since it is necessary to unlock the mechanism using a nail in order to adjust the length of the strand, and to hold the base plate when it is desired to change the length of the bracelet strand. Furthermore, the locking of the mechanism is not entirely secure, since the cover may be unlocked if it becomes caught or if there is a shock when the bracelet is worn.